Thermal spraying is a technique where various thermal spray materials (metals, ceramics and plastics) to be fed into a thermal spray gun are melted with a gas flame or an electric or plasma arc, atomized with a high-pressure gas or inert gas and sprayed on a material to be treated to form a sprayed coating.
The material subjected to the thermal spray has improved corrosion resistance, heat resistance, abrasion resistance and other properties depending upon the properties of the thermal spray material. For example, it is known that thermal spray is effected on the inner periphery of a bore of cylinder blocks of which abrasion resistance is required.
In order to homogeneously spray a thermal spray jet jetted from a thermal spray gun on an inner periphery, the thermal spray has hitherto been effected while rotating the material to be treated. However, the rotation of the material to be treated becomes difficult with an increase in the size of the material to be treated. This has lead to the use of a thermal spray gun having a rotating tip (see U.S. Pat. No. 5,014,916) for the purpose of facilitating the thermal spray on the inner periphery without rotating the material to be treated.
As shown in FIG. 10, a fuel gas, oxygen and compressed air are fed respectively through a fuel gas feed port 8, an oxygen feed port 10 and a compressed air feed port 7 into a thermal spray gun 1 provided on the central axis of the inner periphery of a material 2 to be treated to form a combustion flame. A thermal spray material (a powder) carried from the thermal spray material feed port 9 by a carrier gas is fed into the combustion flame to form a thermal spray jet 4 which is then jetted through the thermal spray gun 1. The tip of the thermal spray gun is rotated by a motor 11 and a belt 12, which are rotating means, and serves to homogeneously spray the thermal spray jet 4 into the material 2 to be treated.